Question

1 (4 pts). Draw the expected major product from the following reaction by placing appropriate groups (H, Br, CH3 on the scaffold). Circle whether the product is achiral or chiral. CH3 CH3 Br2 Br H₃C CH3 Br chiral or achiral a How is it achiral?

please explain why this is achiral and not chiral.

Answer 1

CH3 plane of symmetry - -- H ABARI ---- H3C Br (2R,3S)-2,3-dibromobutane The obtained product is achiral because the chiral centers present in the given molecule have exactly opposite configuration and it also has a plane of symmetry present in it. Hence it becomes a meso compound and hence it is achiral. CH3 Br CH3 3 H3C 3 H3C clockwise oreintation of priority groups and hence configuration is R clockwise oreintation of priority groups, but the least priority group (H) present above the plane and hence configuration is S

The configuration for the both estrogenic centers is R HO Estrogenic center or chiral center is the center that is attached to four different groups to it. In the given molecule, there are two such centers marked with asterisk (*). To know the absolute configuration at chiral carbons (carbons attached with four different groups), the priority of the attached groups has to given by Cahn-Ingold-Prelog (CIP) rules. According to CIP rules the group with highest molecular weight should get first priority (1) followed by the groups with next highest molecular weights. If the attached groups are same in the adjacent atoms, one has to move further to see different atoms. After giving priorties according to CIP rules, if the rotation of the priority groups (from 1st priority group to 3rd priority group) is clock wise then the configuration of that chiral center is R if the rotation of the priority groups (from 1st priority group to 3rd priority group) is anti clock wise then the configuration of that chiral center is S If the least priority group (40 is present above the plane then the configuration of the chiral center should be opposite. That means R becomes S and S becomes HO Clock wise orientation of the priority groups and hence configuration is R HO ZI anti clock wise orientation of the priority groups but the least priority group (H) present above the plane and hence configuration is R